Prevalence of different types of interproximal contacts in the permanent dentition – a study cast evaluation

Background A new classification called OXIS was proposed for categorizing the interproximal contacts of primary molars, modified for the primary canines and its prevalence was established. No such information is available for the permanent dentition. Hence, the aim was to establish the variations in interproximal contacts of the permanent dentition and thereby modify the OXIS classification of primary molars and primary canines to the permanent dentition. Methods We propose a study-cast-based classification of interproximal contacts of the permanent dentition. Three hundred and forty-three pretreatment casts of patients based on an inclusion and exclusion criteria were selected. Contacts of posterior teeth were classified based on OXIS classification of interproximal contacts, and its modification was used for anterior teeth. Results Among the posterior contacts, the ‘O’ type of contact was least prevalent, while most prevalent was the ‘S’ type for second molar-first molar contact, ‘I’ type for the first molar-second premolar contact, and ‘X’ type for the second premolar-first premolar contact. Among the anterior contacts, least prevalent was ‘S1’ type for the first premolar-canine contact, and I type for the canine-lateral incisor and the lateral incisor-central incisor contacts. There was no statistical significance between right- and left-side contacts ( P > 0.05) while significance was seen between maxillary and mandibular contacts ( P < 0.05). Similarity of contacts ranged from 5.17% to 10.05%. Conclusion The OXIS classification is applicable to posterior permanent teeth, and its modification is representative of anterior permanent teeth.


Methods
We propose a study-cast-based classification of interproximal contacts of the permanent dentition.Three hundred and forty-three pretreatment casts of patients based on an inclusion and exclusion
Baranya Shrikrishna Suprabha, Manipal 3. criteria were selected.Contacts of posterior teeth were classified based on OXIS classification of interproximal contacts, and its modification was used for anterior teeth.

Results
Among the posterior contacts, the 'O' type of contact was least prevalent, while most prevalent was the 'S' type for second molar-first molar contact, 'I' type for the first molar-second premolar contact, and 'X' type for the second premolar-first premolar contact.Among the anterior contacts, least prevalent was 'S1' type for the first premolarcanine contact, and I type for the canine-lateral incisor and the lateral incisor-central incisor contacts.There was no statistical significance between right-and left-side contacts (P > 0.05) while significance was seen between maxillary and mandibular contacts (P < 0.05).Similarity of contacts ranged from 5.17% to 10.05%.

Conclusion
The OXIS classification is applicable to posterior permanent teeth, and its modification is representative of anterior permanent teeth.

Amendments from Version 2
The Introduction section has been made more robust with the addition of references.It has also been reinforced in the Introduction section that while there is compelling evidence suggesting that variations in contacts between teeth are important in the development of proximal caries in the primary dentition it would be of clinical interest to assess it in the permanent dentition.Further, in the Inclusion and Exclusion criteria, it has been specified that the casts which were evaluated were pretreatment casts of orthodontic patients.In the Discussion section, the application of the findings of the present study in terms of the prevalence of the various contacts has been discussed.It has been proposed that these contacts would be corrected with orthodontic treatment and thus it would be of clinical interest to compare these findings with the treated occlusion.With the addition of references, the reference order has also been appropriately modified.

Introduction
The six keys to normal occlusion, namely, molar relationship, crown angulation, crown inclination, rotations, tight contacts, and occlusal plane, were proposed by Andrews 1 .The fifth key, tight contacts, refers primarily to the nature of the interproximal contacts.An intact and a well-founded inter proximal contact plays a major role in the periodontal health and stability of the dentition 2 .
Contact areas have been studied and classified in the primary molars as being of four different types, namely, open (O), point contact (X), straight contact (I), and a curved contact (S), and thus the acronym "OXIS" 2 .For the interproximal contacts of the primary canines, a modification of the OXIS classification has recently been reported 3 .While the OXIS classification is of particular significance to the occurrence of dental caries, it would impact class II cavity preparation, placement of stainless steel crowns as well as interproximal reduction (IPR).Existing literature suggests primary teeth which are characterized by broader inter proximal contact areas have a greater susceptibility to caries [4][5][6] .Further, Cortes et al. have reported that in primary molar teeth, if both the proximal surfaces are concave, the caries risk is more 7 .
While contact areas have been studied and classified in the primary dentition, no such information is available for the permanent dentition except that it is listed as the fifth of the six keys to occlusion.With compelling evidence suggesting that variations in contacts between teeth are important in the development of proximal caries in the primary dentition [8][9][10] , it would be of clinical interest to assess it in the permanent dentition.The variations could have orthodontic implications like the stability of orthodontic treatment 11 , magnitude of force application and force distribution from one tooth to another since the interface between adjacent teeth is due to an equilibrium between the compressive force that each tooth exerts on its counterpart and the resisting force which tries to separate them 12 .Also, extraction decisions in orthodontics have been based on post-treatment contacts.First premolars are routinely extracted to maintain first-molar-second-premolar continuity rather than placing the molar adjacent to the first premolar, which is not as anatomically suitable for molar contact 13 .Further research into the types of and variations in interproximal contact areas will elucidate the validity of this decision.Thus, a classification of the interproximal contacts in the permanent dentition would be the first step to providing more information on the orthodontic implications and importance of the fifth key of occlusion.A classification based on study casts would not only ensure simplicity but could also be easily applied during a routine intraoral clinical examination.Hence, the aim was to establish the variations in interproximal contacts of the permanent dentition and thereby modify the OXIS classification of primary molars and primary canines to the permanent dentition and report the prevalence of the same.

Study design and ethics approval
Institutional Ethics Committee, (REF: IEC-NI/19/JUL/70/50) approval was obtained for this cross-sectional retrospective study.Casts of the patients were taken from department records.Written Informed consent was obtained from the patients.
Training and calibration of the examiner.Before the study began in the university orthodontic department, a single dentist VK was extensively trained and calibrated under the supervision of one of the authors of the OXIS classification, to evaluate the contact areas.The calibration process involved a presentation of the classification and theoretical discussions on its use, followed by practical sessions thereon.Finally, a clinical exercise involving examination and re-examination of the same 20 patient study casts (26 intact contacts per patient), comprising 520 intact contacts, was screened by the same primary investigator on two separate occasions after a three-week interlude.The kappa value to test the intra-examiner variability was obtained as 0.82, which reflected a high degree of agreement.

Sample size calculation.
Sample size calculation was based on the data from a pilot study of 780 intact interproximal contacts (30 patient casts) The distribution of the types of contacts in percentage terms was as follows: O type, 16%; X type, 13%; I type, 62%; and S type, 9%.Therefore, with an expected proportion of 9%, relative precision of 20%, and desired confidence level of 95%, the sample size required was 8917 contacts, that is, 343 patient casts.
Inclusion and exclusion criteria.The inclusion criteria were: pretreatment casts of patients with intact contacts, with a full complement of permanent teeth other than third molars, and between the ages of 14 years and 25 years.The exclusion criteria were casts of patients with carious, filled or fractured teeth, occlusal wear and any developmental anomalies affecting the morphology of the tooth (peg laterals, etc.)After an initial screening of 622 patient casts obtained from the records of the Department of Orthodontics (XXX), 343 patient casts that matched the eligibility criteria were selected.The records obtained were from the period 2016 to 2020.

Assessment and evaluation.
The examiner classified not more than 25 patient casts a day in random order.The evaluation was done with the naked eye and natural lighting.These casts were one-to-one replicas without magnification.They were based and placed on a flat table for assessment, and the evaluation was done from a standardized distance.The distance was standardized by placing the casts on a specified table.The distance between the eye line of the primary investigator and the cast was measured to be one foot.These standardizations were applied for all measurements (Figure 1).The assessment of the maxillary and mandibular casts always began with the second molar-first molar interproximal contact on the right quadrant and proceeded across the midline to the left quadrant second molar-first molar interproximal contact.Whenever there was any doubt regarding the quantum of measurement with visual inspection, a Williams probe was used to measure the distance and the contact was graded accordingly.The shape of the evaluated contact was simultaneously entered into the data sheet designed for this study.Third molars were not considered.

Evaluation of posterior tooth contacts.
The maxillary and mandibular posterior teeth were examined by being viewed from the occlusal surface for the shapes of the contact areas.The posterior tooth contacts assessed were three per quadrant, that is, the contact between the mesial aspect of the second molar and the distal aspect of the first molar, up to the contact between the mesial aspect of the second premolar and the distal aspect of the first premolar.This was done for right and left sides and for the maxillary and mandibular casts.The contacts were classified based on the OXIS classification 2 .Briefly, this classification applied 'O', that is, an open contact, if there was no contact between the adjacent teeth, 'X' if there was a point of contact of less than or equal to 1.5 mm, 'I' if there was a straight contact of more than 1.5 mm, and 'S' if there was a curved contact of greater than 1.5 mm between adjacent teeth.
Evaluation of anterior tooth contacts.The maxillary and mandibular anterior teeth were examined by being viewed from the incisal surface for the shapes of the contact areas.Contacts between mesial aspect of first premolar and distal aspect of canine, starting from right side to the corresponding tooth contact on the left side, were assessed.The anterior tooth contacts were classified based on a modification of the OXIS classification 3 , where the 'S' type alone was modified as 'S1' or 'S2'.The contact was classified as 'S' type I (S1) when the tooth was rotated and only one of its surfaces (either proximal or labial/lingual) was in contact with the adjacent tooth.The contact was classified as 'S' type II (S2) when the tooth was rotated and had two surfaces -proximal (mesial/distal) and labial or lingual was in contact with the adjacent tooth.
Scoring.For posterior contacts, a score of 0 was given for the open (O) contacts 1 for 'X', 2 for 'I' and 3 for 'S'.For anterior contacts, the 'O', 'X', and 'I' contacts were also scored as 0, 1, and 2, but the 'S' type 'I' was scored as 3, and the 'S' type II was scored as 4. Figure 2-Figure 6 are illustrations of the OXIS patterns of the interproximal contacts, with their corresponding clinical images and their equivalent stone models.

Statistical analysis.
Statistical analysis was performed with SPSS 19.0 software (SPSS, Chicago, Ill., USA).Given that SPSS is proprietary, for the purpose of reproducibility, we can recommend PSPP 1.6.2. GNU PSPP or Microsoft Excel as free alternatives.Numbers and percentages were used to express the prevalence of the types of contact areas.In total, 8918 contacts, that is, 4116 posterior and 4802 anterior contacts were evaluated.To determine the association of contact areas in each quadrant across gender chi square test was applied.McNemar's test was used to assess intra-and interarch variability.A P value of less than 0.05 was deemed to indicate statistical significance.

Prevalence and percentages
Of the 343 patients, 190 were female and 153 were male, with ages ranging from 14 years and 3 months to 23 years and 9 months (mean age, 20 years and 3 months).Table 1-Table 3 summarize the prevalence and percentages of contacts in the permanent dentition according to arch, side, and gender.Among the posterior contacts, the 'O' type was the least prevalent, while the 'S' type was the most prevalent among the second molar-first molar contacts, the 'I' type among the first molar-second premolar contacts, and the 'X' type among the second premolar-first premolar contacts.Among the anterior contacts, the least prevalent was the 'S1' type for the first premolar-canine contact, and the 'I' type for the canine-lateral incisor contact and the lateral incisor-central incisor contact.The most prevalent was the 'X' type among all anterior contacts except the caninelateral incisor contact, where the 'S2' type was most prevalent.There was no statistical significance between the right-and left-side contacts (P > 0.05).However, statistical significance was seen between the maxillary and mandibular contacts (P < 0.05).Gender vs right maxilla: χ 2 = 2.76, P = 0.43.Gender vs left maxilla: χ 2 = 0.14, P = 0.98.Gender vs right mandible: χ 2 = 2.63, P = 0.45.Gender vs left mandible: χ 2 = 2.74, P = 0.43.Gender vs right maxilla: χ 2 = 1.26,P = 0.74.Gender vs left maxilla: χ 2 = 11.22,P = 0.01.Gender vs right mandible: χ 2 = 9.03, P = 0.03.Gender vs. left mandible: χ 2 = 1.76,P = 0.62.

Similarities of contacts
The similarities of contacts in all four quadrants in the posterior segment were 5.17% for the second molar-first molar contacts, 5.47% for the first molar-second premolar contacts, and 8.02% for the second premolar-first premolar contacts.
The similarities of contacts in all four quadrants in the anterior segment were 5.32% for the premolar-canine contact, 4.08% for the canine-lateral incisor contact, and 4.88% for the lateral incisor-central incisor contact.When the midline contacts were assessed, 10.05% of the samples had similar contacts in the maxilla and the mandible.

Intra-arch, interarch, and gender comparisons
When the intra-arch comparison (right vs left) was performed for the same individual, there was a statistically significant difference (P < 0.05) for the 'X', 'I', and 'S' types of contacts on the right and left sides for second molar-first molar contacts, while there was a statistically significant difference for all four contact types for first molar-second premolar contacts (P < 0.05).No statistically significant associations were found for the posterior and anterior contacts when gender was compared in individual quadrants (P >0.05), except for the first premolar-canine contacts (gender vs right and left maxilla and right mandible) and for the canine-lateral incisor contacts (gender vs left maxilla) (P < 0.05).

Discussion
While Andrews' six keys to occlusion are the objectives of successful orthodontic treatment 1 , there is only minimal literature on the fifth key, that is, interproximal contacts.Previous literature on the primary dentition has described the contacts as open/closed [14][15][16][17][18][19] or as convex and concave 7 .To the best of the authors' knowledge, there is no existing classification for inter proximal contacts of the permanent teeth.The impetus for this proposed classification was based on the sequence of manuscripts on OXIS contacts and their reports on the association/ susceptibility of various patterns of contacts to caries 2,3,8,[20][21][22] .This present retrospective study of ours assessed the interproximal contact variations of permanent teeth and aimed to propose a classification which would be simple yet comprehensive.
The prevalence of the contacts revealed that the broader contacts, that is, the 'I' and 'S' types, were predominantly associated with the posterior contacts, while the anterior contacts were more of the S1 and S2 types.The 'O' type of contact was more commonly seen in the maxilla and warrants further research.While there was minimal difference between gender in the types of posterior contacts, there was an alteration in the distribution of the types of contacts between the maxilla and the mandible.This could not be compared with other studies due to a lack of previous data available in the literature.Approximately 90% of the patients had more than one type of contact in different quadrants.This would indicate that the contact is established by local factors and is an unexplored aspect which may be critical in the development of single or random caries lesions.
The types of contacts could play a substantial role in plaque buildup and caries development.When compared with the 'O' and 'X' types the 'I' and 'S' types of contacts would be inaccessible for mechanical cleansing 2 .Muthu et al., in their retrospective cohort study evaluated the caries risk of the contacts of primary molars based on the OXIS classification and reported that the S and I types of contacts had higher odds of caries development compared with the X and O types 8 .Not only would orthodontic treatment alter the contacts, but also procedures like interproximal reduction and extractions would alter the contact and its type.Therefore, future studies should focus on the long-term stability of the types of contacts following orthodontic treatment.
Stappert et al. 23 reported that the quantum of the contact area decreased progressively from 4mm at the midline contact to 1.5mm at the canine premolar contact.They reported that contact areas, not contact points, were observed between neighbouring maxillary anterior teeth.The findings of our study were not in consonance with Stappert et al. 23 While our study had a greater prevalence of "X" contacts, and therefore point contacts, the reasonfor this variation could be because Stappert et al. 23 assessed the interproximal contacts on patients who had no crowding or spacing in the anterior teeth.Thus, it would not be representative of our sample which hadmalocclusion and therefore malaligned teeth.Further, our study was a linear measurement based on visual observation of the interproximal contact while Stappert et al. 23 quantified the area based on mathematical calculations.
By far, the most significant orthodontic clinical implication of the type of contact area, especially with fixed appliance therapy is that it could be a determining factor for the development of proximal caries.This has been further established in controversial literature regarding the relationship between dental caries and orthodontic treatment, in that, while orthodontic treatment has been implicated in alteration of the oral environment by providing retention sites for dental plaque 24 and therefore increasing the risk of caries development [25][26][27] , other authors believe that fixed orthodontic appliances may not be the singular factor in the development of caries in the patient undergoing fixed orthodontic treatment 28,29 .It could therefore be considered that the type of contact would make a difference in this varying literature.It is plausible to hypothesize that teeth could be at higher risk for caries formation in patients with fixed appliances where broader contacts ('I' and 'S' types) and rotated teeth ('S1' and 'S2') are present.Moreover, contacts would be corrected with orthodontic treatment and it would be of clinical interest to compare these findings with the treated occlusion.
The strengths of our study are that it provides the variations in the Andrews' fifth key i.e. inter proximal contacts of permanent teeth for the first time in the literature and it has assessed the types of contact areas in permanent teeth with a large sample of 8918 intact interproximal contacts and classified them according to OXIS criteria.

References
A major limitation is that the sample was obtained from patients with malocclusion and hence may not be reflective of the general population.
The directions of future research are the following: • Longitudinal assessment of the change in interproximal contacts with age and eruption of the third molars need to be studied.
• Stability/Relapse of the treated occlusion with different interproximal contact types.
• Incidence of proximal caries with different interproximal contact types in the permanent dentition and in patients undergoing orthodontic treatment.
• Variation in interproximal contacts in different malocclusions (namely Class I, Class II, Class III etc.) and different ethnic populations.

Conclusion
The OXIS classification of interproximal contacts is applicable to posterior and anterior permanent teeth.Among the posterior contacts, the 'O' type of contact was the least prevalent, while 'I' type was the most prevalent.Among the anterior contacts, the 'I' type of contact was the least prevalent, while the 'X' type was the most prevalent.No significant associations were found for the contacts when gender was compared in individual quadrants (P > 0.05).Similarity of contact in all four quadrants ranged from 5.17% to 10.05%.

Data availability
Open Science Framework: An evaluation of the interproximal contacts of the permanent dentition-A study cast based classification.
Data is available under the terms of the Data are available under the terms of the Creative Commons Zero "No rights reserved" data waiver (CC0 1.0 Public domain dedication).

Baranya Shrikrishna Suprabha
Manipal Academy of Higher Education, Manipal, Karnataka, India While I appreciate the novelty of the study objective, application of OXIS classification in permanent dentition, the vivid presentation in the introduction, results and discussion section, some queries remain regarding the methods section: In the inclusion criteria, add that the casts were of patients seeking treatment for 1.
malocclusion, if pre-treatment casts were used.Please specify whether pre-treatment/posttreatment casts were used.While the code S2 is designated for anterior teeth contact with minor rotation, how was the coding considered in case of mild rotation of posterior teeth? 2.
"Whenever there was any doubt regarding the quantum of measurement with visual inspection, a Williams probe was used to measure the distance and the contact was graded accordingly."The description of measurement needs to be more specific.How was 1.5mm contact (As per OXIS) measurement done just by visual examination, without measuring each cast?

3.
How was the accuracy of the examiner performing visual examination on orthodontic casts and classifying the contacts ensured?How was the reliability ensured?Was any calibration done with an expert examiner?Please provide inter and intra-rater reliability values.

4.
Were the dental casts anonymized during measurement?How was the examiner bias minimized regarding gender and age variation of the patients whose dental casts were examined?

5.
I understand that the use of dental casts of patients with malocclusion is a major study limitation.Please add in discussion, the applicability of the study findings (in terms of prevalence of various contacts obtained in the study) 6.
In the introduction, the sentence "The variations in the contact areas of the permanent dentition might alter caries susceptibility and have orthodontic implications affecting the magnitude of force application, force distribution from one tooth to another and stability of orthodontic treatment" requires a reference.

Are the conclusions drawn adequately supported by the results? Yes
Competing Interests: No competing interests were disclosed.

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.
Author Response 20 Jul 2024

M KIRTHIGA
In the inclusion criteria, add that the casts were of patients seeking treatment for malocclusion, if pre-treatment casts were used.Please specify whether pretreatment/post-treatment casts were used.

1.
Response: We thank the Reviewer for this suggestion.We have modified the sentence by specifying that pre treatment casts were used.From Inclusion and exclusion criteria.The inclusion criteria were: casts of patients with intact contacts, with a full complement of permanent teeth other than third molars, and between the ages of 14 years and 25 years.To Inclusion and exclusion criteria.The inclusion criteria were: pretreatment casts of patients with intact contacts, with a full complement of permanent teeth other than third molars, and between the ages of 14 years and 25 years.
While the code S2 is designated for anterior teeth contact with minor rotation, how was the coding considered in case of mild rotation of posterior teeth? 1.
Response: While we are grateful to the Reviewer for this query, the rotations of posterior teeth were covered within the OXIS classification.Posterior teeth with broader contact were observed to have S and I type contacts while those with rotations had X type contacts.No changes made."Whenever there was any doubt regarding the quantum of measurement with visual inspection, a Williams probe was used to measure the distance and the contact was graded accordingly."The description of measurement needs to be more specific.How was 1.5mm contact (As per OXIS) measurement done just by visual examination, without measuring each cast? 1.
Response: While we appreciate the intent of the Reviewer to strengthen the assessment methodology, we would like to reinforce that we used Williams probe only for the borderline cases which could not be categorized with certainty on visual inspection.No changes made.How was the accuracy of the examiner performing visual examination on orthodontic casts and classifying the contacts ensured?How was the reliability ensured?Was any calibration done with an expert examiner?Please provide inter and intra-rater reliability values. 1.

Response:
We acknowledge the query of the Reviewer.The inter examiner variability a part of the training and calibration process and was 0.92.The reliability was ensured by training and calibration with an expert examiner.The intra examiner reliability data has been provided in the manuscript.This information is available in the paragraph) titled "Training and calibration of the examiner."(Page 4 -appended and highlighted below for the Reviewer's convenience).Before the study began in the university orthodontic department, a single dentist VK was extensively trained and calibrated under the supervision of one of the authors of the OXIS classification, to evaluate the contact areas.The calibration process involved a presentation of the classification and theoretical discussions on its use, followed by practical sessions thereon.Finally, a clinical exercise involving examination and reexamination of the same 20 patient study casts (26 intact contacts per patient), comprising 520 intact contacts, was screened by the same primary investigator on two separate occasions after a three-week interlude.The kappa value to test the intra-examiner variability was obtained as 0.82, which reflected a high degree of agreement.No changes made.
Were the dental casts anonymized during measurement?How was the examiner bias minimized regarding gender and age variation of the patients whose dental casts were examined? 1.

Response:
We are obliged to the Reviewer for the query.The Primary Investigator assessed the casts based on the Out Patient Registration number.This enabled anonymization to the patient details like gender and age, thus ensuring minimization of examiner and observer bias.No changes made.I understand that the use of dental casts of patients with malocclusion is a major study limitation.Please add in discussion, the applicability of the study findings (in terms of prevalence of various contacts obtained in the study) 1.

Response:
We are obliged to the reviewer for this suggestion.We have modified the Discussion section accordingly.From 'It is plausible to hypothesize that teeth could be at higher risk for caries formation in patients with fixed appliances where broader contacts ('I' and 'S' types) and rotated teeth ('S1' and 'S2') are present'.Moreover, contacts would be corrected with orthodontic treatment and it would be of clinical interest to compare these findings with the treated occlusion.
In the introduction, the sentence "The variations in the contact areas of the permanent dentition might alter caries susceptibility and have orthodontic implications affecting the magnitude of force application, force distribution from one tooth to another and stability of orthodontic treatment" requires a reference.

1.
Response: We are indebted to the reviewer for this suggestion.We have edited the sentence and have added the following references.From 'The variations in the contact areas of the permanent dentition might alter caries susceptibility and have orthodontic implications affecting the magnitude of force application, force distribution from one tooth to another, and stability of orthodontic treatment' to 'With compelling evidence suggesting that variations in contacts between teeth are important in the development of proximal caries in the primary dentition [8][9][10] , it would be of clinical interest to assess it in the permanent dentition.The variations could have orthodontic implications like the stability of orthodontic treatment 11 , magnitude of force application and force distribution from one tooth to another since the interface between adjacent teeth is due to an equilibrium between the compressive force that each tooth exerts on its counterpart and the resisting force which tries to separate them 12

Tarulatha R. Shyagali
Orthodontics and Dentofacial Orthopedics, M R Ambedkar Dental College and Hospital, Bengaluru, Karnataka, India I feel the manuscript requires no further changes.

If applicable, is the statistical analysis and its interpretation appropriate? Yes
Are all the source data underlying the results available to ensure full reproducibility?Yes

Are the conclusions drawn adequately supported by the results? Yes
Competing Interests: No competing interests were disclosed.

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard. Version 1
Reviewer Report 08 September 2023 https://doi.org/10.21956/wellcomeopenres.21035.r65764 © 2023 Garg S. This is an open access peer review report distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Shalini Garg
Pediatric and Preventive Dentistry, Shree Guru Gobind Singh Tricentenary University, Gurugram, Haryana, India Sample was taken from a specific group of subject requiring orthodontic treatment.(BIASED) 1.
Type of malocclusion and molar relationship will affect type of inter-proximal contacts.It can not be applied to all population groups.

2.
Presence absence and eruption status of permanent third molar will affect type of contacts depending upon age of the patient.

3.
Presence of hidden inter-proximal caries can affect the OXIS classification specially with broader contact area.

4.
The inclusion and exclusion criteria need to be thoroughly revised .

5.
The exact measurement of less or more than 1.5 mm doesn't seem possible with naked eyes.

Are sufficient details of methods and analysis provided to allow replication by others? Partly
If applicable, is the statistical analysis and its interpretation appropriate?I cannot comment.A qualified statistician is required.

Are the conclusions drawn adequately supported by the results? Partly
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Pediatric dentistry , Caries research, Dental trauma I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.
Author Response 14 Oct 2023

Reviewer 2 Queries
Sample was taken from a specific group of subject requiring orthodontic treatment.(BIASED) 1.
We thank the reviewer for this important observation.We have modified the last paragraph of Discussion, From The possible limitations of this study are that the included samples (study casts) are from the patients who reported for orthodontic treatment and hence would have had increased incidence of malpositions like crowding, spacing, rotations etc.To A major limitation is that the sample was obtained from patients with malocclusion and hence may not be reflective of the general population.a. Type of malocclusion and molar relationship will affect type of inter-proximal contacts.

1.
Kindly refer to the answer given to Question no.3a of Reviewer 1. b.It can not be applied to all population groups.We are in consonance with the comment of the Reviewer.Therefore, we have added it to the directions of future research.Kindly refer to the answer given to Question no.3a of Reviewer 1.
Presence absence and eruption status of permanent third molar will affect type of contacts depending upon age of the patient.

1.
We admit that it would be scientifically relevant to assess the role of third molar in the change in interproximal contacts.Therefore we have added it to the directions of future research.Kindly refer to the answer given to Question no.3a of Reviewer 1.
Presence of hidden inter-proximal caries can affect the OXIS classification specially with broader contact area. 1.
While we thank the reviewer for this observation, based on the research teams prior experience on OXIS studies on primary teeth 1,2 where bite wing radiographs were also used to assess the presence of caries, hidden caries did not contribute to change in the type of interproximal contact.However, if the hidden caries progresses to cavitation (Class II), scoring of the contact type becomes challenging.References Variations in primary molar contact and approximal caries in children: A 3-year prospective cohort study.Kirthiga M, Muthu MS, Kayalvizhi G, Mathur VP, Jayakumar N. Pediatr Dent 2023;45(5):434-9.E48-E50. 1.

2.
The inclusion and exclusion criteria need to be thoroughly revised .1.
The inclusion and exclusion criteria have been revised.Kindly refer to the answer given to Question no.6b of Reviewer 1.
The exact measurement of less or more than 1.5 mm doesn't seem possible with 1.
naked eyes.We are in concurrence with the observation of the Reviewer.Kindly refer to the answer given to Question no. 2 of Reviewer 1.

Competing Interests:
No competing interests were disclosed.

Tarulatha R. Shyagali
Orthodontics and Dentofacial Orthopedics, M R Ambedkar Dental College and Hospital, Bengaluru, Karnataka, India Thank you very much for asking me to review this paper, I congratulate the authors for their efforts in pursuing this research, although paper is well written, I have a few queries to make related to this paper; The authors mention that they used the standardized distance for measurement, could they specify how much is the standardized distance and how did they manage to achieve the same since they were viewing the casts from top/occlusal view?Kindly provide the photo of the assessment if possible. 1.
Since quantifying less than 1.5 and more than 1.5 is so difficult, how did authors manage to achieve it by visual inspection, was there a possibility of using any tool to overcome this drawback? 2.
Although the authors mention that the study was flawed in taking up the cast from department of orthodontics, But I still would be commenting on the fact that, authors could have set the stringent inclusion criteria, so that they could have selected near to ideal or normal occlusion casts.Because slippage of the contact is so common in malocclusion casts.Further, authors give S1 and S2 type of contacts in anterior teeth, which is commendable, however again quantifying the same will be difficult.

3.
Apart from this, if we know what is normally seen in ideal or normal occlusion we could be better prepared to keep the normal contacts intact and treat the abnormal contacts or take precaution to prevent the unwanted side effects from them.

4.
Rather the classification, study was more of the assessment of the prevalence of different types of interproximal contacts.So, I feel authors should take a call on changing the title of the article to suit their study results

5.
Inclusion and exclusion criteria were not set properly, as following major criteria were not taken into consideration; a. Severity of the malocclusion determines the interproximal contact area type, authors failed to set the selection criteria for this.
b.A filled or carious or traumatic tooth would obliviously affect the interproximal contact point, authors fail to consider this as well.
c. Was there in criteria set to exclude periodontally compromised patients?would this have any affect on your findings.

6.
Will the shape of tooth determine the types of interproximal contact area, was there any consideration given to this factor?7.
Authors finding suggests that, the prevalence for '

M KIRTHIGA
The authors mention that they used the standardized distance for measurement, could they specify how much is the standardized distance and how did they manage to achieve the same since they were viewing the casts from top/occlusal view?Kindly provide the photo of the assessment if possible.We thank the Reviewer for the valuable suggestion and a photo of the assessment has been provided.(Figure 1).The distance was standardized by placing the cast on a specified table.The distance between the eye line of the primary investigator and the cast was measured to be one foot.These standardizations were applied for all measurements. 1.
We have added a new figure, (Figure 1) with appropriate legends.Figure 1: Image depicting standardization of distance during interproximal contact assessment.Changes made in Materials and Methods, From They were based and placed on a flat table for assessment, and the evaluation was done from a standardized distance.To They were based and placed on a flat table for assessment, and the evaluation was done from a standardized distance.
The distance was standardized by placing the casts on a specified table.The distance between the eye line of the primary investigator and the cast was measured to be one foot.These standardizations were applied for all measurements.Since quantifying less than 1.5 and more than 1.5 is so difficult, how did authors manage to achieve it by visual inspection, was there a possibility of using any tool to overcome this drawback? 1.
We are in concurrence with the observation of the Reviewer.Whenever there was any doubt regarding the quantum of measurement with visual inspection, a Williams probe was used to measure the distance and the contact was graded accordingly.Changes made in Materials and Methods, From The assessment of the maxillary and mandibular casts always began with the second molar-first molar interproximal contact on the right quadrant and proceeded across the midline to the left quadrant second molar-first molar interproximal contact.To The assessment of the maxillary and mandibular casts always began with the second molar-first molar interproximal contact on the right quadrant and proceeded across the midline to the left quadrant second molar-first molar interproximal contact.Whenever there was any doubt regarding the quantum of measurement with visual inspection, a Williams probe was used to measure the distance and the contact was graded accordingly.a.Although the authors mention that the study was flawed in taking up the cast from department of orthodontics, But I still would be commenting on the fact that, authors could have set the stringent inclusion criteria, so that they could have selected near to ideal or normal occlusion casts.

1.
This suggestion by the reviewer would have definitely strengthened the inclusion criteria.However, since we planned a separate study for assessing the interproximal contacts in normal occlusion casts, it was not part of the eligibility criteria.We accept and concur with the Reviewer's suggestion.We will able to provide an answer to this question with a separate study on ideal or normal occlusion which has been planned.It has been added to the directions of future research.Kindly refer to the answer for Question No. 3a Rather the classification, study was more of the assessment of the prevalence of different types of interproximal contacts.So, I feel authors should take a call on changing the title of the article to suit their study results.

1.
We are in concurrence with the Reviewer's reasoning on the need for Title change.We propose to change the Title, From "An evaluation of the interproximal contacts of the permanent dentition-A study cast based classification" To "Prevalence of different types of interproximal contacts in the permanent dentition -a study cast evaluation."Inclusion and exclusion criteria were not set properly, as following major criteria were not taken into consideration; 1.
Severity of the malocclusion determines the interproximal contact area type, authors failed to set the selection criteria for this. 1.
We are grateful to the reviewer for pointing out this important parameter.While we do agree that malocclusion type would have an impact on the type of contacts, we did not consider the malocclusion severity/classification in the eligibility criteria as we had planned a separate study on the prevalence of the various types of interproximal contacts and different malocclusions.Kindly refer to the answer for Question No. 3a A filled or carious or traumatic tooth would obliviously affect the interproximal 1.
contact point, authors fail to consider this as well.We acknowledge and are grateful to the Reviewer for the observation.Though filled, carious and traumatic teeth were not mentioned as part of the exclusion criteria, they were excluded from the study.We have now added them in the exclusion criteria.Changes made in Materials and Methods From The exclusion criteria were any occlusal wear and any developmental anomalies affecting the morphology of the tooth (peg laterals, etc.) To The exclusion criteria were casts of patients with carious, filled or fractured teeth, occlusal wear and any developmental anomalies affecting the morphology of the tooth (peg laterals, etc.) Was there in criteria set to exclude periodontally compromised patients?would this have any affect on your findings. 1.
We concede that a compromised periodontium might affect the interproximal contatcts.
With the study casts, a periodontal evaluation was difficult.Hence the periodontal status was not considered.
Will the shape of tooth determine the types of interproximal contact area, was there any consideration given to this factor? 1.
We endorse the Reviewer's question.Yes, the shape of the tooth would affect the contact.However, teeth with anomalies affecting their morphology were part of the exclusion criteria.The exclusion criteria were the presence of caries, any occlusal wear and any developmental anomalies affecting the morphology of the tooth (peg laterals, etc.).Authors finding suggests that, the prevalence for 'x' type contact was more in midline teeth, lateral incisors and central incisors, We are grateful to the Reviewer for bringing this important study to our attention.The findings of Stappert et al have been added in the "Discussion" section of our manuscript.Changes made to Discussion -(Paragraph added and References changed) Stappert et al 19 reported that the quantum of the contact area decreased progressively from 4mm at the midline contact to 1.5mm at the canine premolar contact.They reported that contact areas, not contact points, were observed between neighbouring maxillary anterior teeth.The findings of our study were not in consonance with Stappert et al. 19 While our study had a greater prevalence of "X" contacts, and therefore point contacts, the reason for this variation could be because Stappert et al 19 assessed the interproximal contacts on patients who had no crowding or spacing in the anterior teeth.Thus, it would not be representative of our sample which had malocclusion and therefore malaligned teeth.Further, our study was a linear measurement based on visual observation of the interproximal contact while Stappert et al 20 quantified the area based on mathematical calculations.

Figure 1 .
Figure 1.Image depicting standardization of distance during interproximal contact assessment.

Figure 3 .
Figure 3. Representative cast images and their equivalent clinical photographs of the interproximal contacts of the maxillary posterior region.

Figure 4 .
Figure 4. Representative cast images and their equivalent clinical photographs of the interproximal contacts of the mandibular posterior region.

Figure 6 .
Figure 6.Representative cast images and their equivalent clinical photographs of the interproximal contacts of the mandibular anterior region.

Figure 5 .
Figure 5. Representative cast images and their equivalent clinical photographs of the interproximal contacts of the maxillary anterior region.

Reviewer Report 13
June 2023 https://doi.org/10.21956/wellcomeopenres.21035.r58270© 2023 Shyagali T. This is an open access peer review report distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Is the work clearly and accurately presented and does it cite the current literature? Yes Is the study design appropriate and is the work technically sound? Partly Are sufficient details of methods and analysis provided to allow replication by others? Partly If applicable, is the statistical analysis and its interpretation appropriate? Yes Are all the source data underlying the results available to ensure full reproducibility? Partly Are the conclusions drawn adequately supported by the results? Yes Competing Interests:
x' type contact was more in midline teeth, lateral incisors and central incisors, but article by Stappert et al., suggests that "Contact areas, not contact points, were observed between neighboring maxillary anterior" teeth.( Stappert, Christian & Tarnow, Dennis & Tan-Chu, Jocelyn & Chu, Stephen.(2010).Proximal Contact Areas of the Maxillary Anterior Dentition.The International journal of periodontics & restorative dentistry.30.471-7.).Authors can give their feedback on the same.No competing interests were disclosed.

have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.
It has been incorporated into the directions of future research.Changes made in Discussion, From Future research should involve longitudinal studies to evaluate the stability/relapse as well as the incidence of proximal caries in patients undergoing orthodontic treatment based on the OXIS classification for permanent dentition.ToThe directions of future research are the following:Longitudinal assessment of the change in interproximal contacts with age and eruption of the third molars need to be studied.Incidence of proximal caries with different interproximal contact types in the permanent dentition and in patients undergoing orthodontic treatment.Because slippage of the contact is so common in malocclusion casts.Further, authors give S1 and S2 type of contacts in anterior teeth, which is commendable, however again quantifying the same will be difficult.Although categorising S1 and S2 type of contacts is little more complex than O, X and I, it is doable because S1 contact involves one surface and S2 involves two surfaces.By taking a close look at the interproximal contact, we could identify and define S1 and S2.For the reviewer's ease, the definition is attached below. 1 S1: When anterior tooth is rotated and only one of its surfaces (either proximal surface or labial/lingual surface) is contacting the adjacent tooth S2: When anterior is rotated and has two of its surfaces -proximal surface (mesial/distal) and labial or lingual surface contacting the adjacent tooth Reference 1.Aarthi J, Muthu M, Kirthiga M and Kailasam V. Modified OXIS classification for primary canines.Wellcome Open Res 2022, 7:130Apart from this, if we know what is normally seen in ideal or normal occlusion we could be better prepared to keep the normal contacts intact and treat the abnormal contacts or take precaution to prevent the unwanted side effects from them 1.